The present invention relates to the technology which may be effectively applied to a power supply device to generate a DC voltage and moreover to a switching regulator which is required to have the excellent transient response characteristic for change of output current, for example, to the technology which may be effectively applied to a power supply device to be mounted to a system which results in large variation of current dissipation.
In recent years, a microprocessor is often mounted as a system control device into an electronic device. Moreover, an operation frequency of the microprocessor (hereinafter, referred to as CPU) tends to be more and more increased and the maximum operation current also increases depending on increase in the operation frequency. For a portable electronic device or the like comprising a built-in CPU, a system is often employed, in which a battery voltage is stepped up or down with a switching regulator to supply the operation current to the CPU, but since the battery is very much consumed in this system, when operation of the CPU is not required, the entire circuit of the CPU or the partial circuit thereof is stopped to operate. Therefore, changing range of current dissipation of the CPU tends to increase with increase of the maximum operation current of the CPU. Therefore, as a power supply device to supply the operation current to the CPU, those having excellent transient response characteristic for change of output current have been required.
As a switching regulator having excellent transient response characteristic, the regulator called the hysteresis current mode control system regulator is known (for example, U.S. Pat. No. 5,825,165).
The proposed switching regulator of the hysteresis current control system comprises a current sense resistor connected in series to a coil for detecting current flowing through the coil and an error amplifier for outputting a current proportional to an error voltage between the voltage (feedback voltage) obtained by dividing an output voltage with a resistance dividing circuit and the reference voltage. The switching regulator of the structure described above compares an error voltage expressed with product of a value of the resistor connected between a connecting node of the coil and sense resistor and an output terminal of the error amplifier and an output current of the error amplifier with an output voltage with a comparator having the hysteresis characteristic and switches a main switch, which supplies a current to the coil when a voltage-drop at the sense resistor exceeds “error voltage+hystereris voltage”, to OFF from ON and also switches a synchronous switch, which operates to reduce a current to the coil synchronously with the main switch, to ON from OFF. Moreover, this switching regulator switches the main switch to ON from OFF when the voltage-drop at the sense resistor becomes lower than the error voltage, and also controls the output voltage to the constant value by turning the synchronous switch to OFF from ON.
Such switching regulator of the hysteresis current mode control system is capable of maintaining the output voltage to the constant value through quick response against change of the output current by elongating the ON period of the main switch when the output current increases and shortening the ON period of the main switch when the output current decreases, in order to provide the feedback effect to elongate the ON period of the synchronous switch.